Vent for core boxes and the like

ABSTRACT

A vent comprising elongated flow passageways through a thin sheet having thin fingers forming at least one of the two opposite side edges of the flow passageway with the top surface of the fingers being generally parallel with the top surface of the sheet. The width of the flow passageways is less than the particle size of the material to be screened from the passing gas, and the fingers are cantilevered, preferably from adjacent one end for maximum flexibility of the fingers. The flexing of the fingers provides a self-cleaning action which may be produced by the passage of gases through the passageways or may be produced by a change in temperature. The sheet material preferably has a thickness that is approximately no greater than the particle size of the material being screened, and in the preferred embodiment, the fingers are made integral with the sheet. This is accomplished by forming an irregular opening through the sheet material, which opening has a width that is less than the particle size of the material to be retained. This opening in some instances will be tapered to provide greater width adjacent the bottom side of the sheet than adjacent the top side of the sheet, and the vents are preferably made by etching out the irregular opening with an acid.

Unite States Patent [7 2] Inventor Charles W. Barrett 2401 S. WayneRoad, Westland, Mich. 48185 [21] Appl. No. 48,935 [22] Filed June 19,1970 [45] Patented Jan.4,1972

Continuation of application Ser. No. 744,143, July 11, 1968, nowabandoned. This application June 19, 1970, Ser. No. 48,935

[54] VENT FOR CORE BOXES AND THE LIKE 22 Claims, 9 Drawing Figs.

[52] US. Cl 164/410 [51] 1nt.Cl B22c 23/00 [50] Field of Search 164/410,234

[56] References Cited UNITED STATES PATENTS 2,238,506 4/1941 Rienacker164/410 2,482,330 9/ 1949 Dudzinski.... 164/410 3,188,701 6/1965Mc1ntyre.. 164/410 3,214,803 11/1965 Amt 164/410 3,529,656 9/1970 Levy164/410 X u q I I a I,

Primary ExaminerRobert D. Baldwin Assistant Examiner.lohn S. BrownAttorney-William P. Hickey ABSTRACT: A vent comprising elongated flowpassageways through a thin sheet having thin fingers forming at leastone of the two opposite side edges of the flow passageway with the topsurface of the fingers being generally parallel with the top surface ofthe sheet. The width of the flow passageways is less than the particlesize of the material to be screened from the passing gas, and thefingers are cantilevered, preferably from adjacent one end for maximumflexibility of the fingers. The flexing of the fingers provides aself-cleaning action which may be produced by the passage of gasesthrough the passageways or may be produced by a change in temperature.The sheet material preferably has a thickness that is approximately nogreater than the particle size of the material being screened, and inthe preferred embodiment, the fingers are made integral with the sheet.This is accomplished by forming an irregular opening through the sheetmaterial, which opening has a width that is less than the particle sizeof the material to be retained. This opening in some instances will betapered to provide greater width adjacent the bottom side of the sheetthan adjacent the top side of the sheet, and the vents are preferablymade by etching out the irregular opening with an acid.

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minnow m2 3.831.918

SHEET 1 OF 2 IN VENTUR. Ear/e L 6 PATENIED JAN. 4 B72 SHEET 2 OF 2 VENTFOR CORE BOXES AND THE LIKE This application is a continuation of Ser.No. 744,l43, filed July I l, 1968, now abandoned.

BACKGROUND OF THE INVENTION In the founding art, cavities are producedin cast metals by means of sand temporarily held together by a binder toproduce what is known as a core. The molten metal is poured around thecore and is allowed to solidify. The binders used are temporary and canbe decomposed, usually by prolonged treatment and oxidation. Thesolidified metal having the core therein is subjected to conditionswhich decompose the binder, usually prolonged heating in air, followingwhich the sand is shaken out of the cast metal body through one or moresmall openings.

The cores are produced in molds comprising two or more pieces usuallytwo which can be disassembled to remove the core once the binder hashardened. The cores are produced by assembling the portions of the moldto provide an enclosure whose cavity corresponds in shape to the shapeof the core desired. The cavity is filled with sand and binder, thebinder is hardened, and the mold is disassembled to remove the finishedcore. In some instances the binder is a powder that is mixed with thesand that is forced into the mold cavity. In other instances, the sandis coated with the binder and the coated sand is forced into the moldcavity. The sand and binder may be tamped into the mold cavity, but inthe process with which we are concerned, the sand is blown into the moldcavity by means of compressed air. The air displaced by the sand as wellas any compressed air reaching the cavity must be vented therefrom inorder to be sure that no air pockets or soft spots exist in the finishedcores. The air is vented through screening devices commonly called ventswhich retain the sand and binder while allowing the escape of the air.These vents are subject to sand abrasion, which can be quite severe inthose instances where some of the sand particles are forced through theopenings of the vent. In all prior art vents with which I am concerned,sand and binder tends to accumulate in the air passages of the vent.Sand particles just slightly larger than the openings through the ventbecome wedged in the opening, and this wedging process continues untilsubstantially all of the openings through the vent become plugged. Mostmolds are designed with only sufiicient venting capacity to makesatisfactory molds when the vents are in an unplugged condition, andconsequently the quality of the cores deteriorate when the vents startto become plugged. In many instances the core-producing process iscarried on in automatic machinery and the plugged condition of the ventsis not ascertained until a sizable production of nonusable cores hasbeen produced.

Air blown cores are made by a number of different processes. In onecommonly used process, an oil such as linseed oil is used to coat thesand which is air blown into the molds. The unhardened cores made withoxidizing oil is removed and placed in dryers which allows aircirculation therethrough. The dryers conmining the cores are put inovens where oxidization of the binder takes place to set the binder to arigid condition. This is sometimes called a green-sand-molding P ocess.

Another type of process commonly used is called the hot bo'x process. Inthe hot box process, sand either coated with or mixed with athermosetting resin, usually a phenol-formaldehyde is air blown into thecavity of the mold. The mold is heated, and after the resin and sand hasbecome stationary against the mold cavity surface for a few seconds, theresin is transformed into its therrnoset condition, and thereafter themold is split and the core removed form the mold cavity. Other types ofthermosetting resins can be used, as for example phenol-furfural resins,etc.

Air blown cores can also be made by several cold processes wherein a gasis caused to pass through the core to set up the binder after the sandand binder are blown into the mold cavity. In one such process, sand iscoated with sodium silicate binder and this binder coated sand is thenblown into the mold cavity. Thereafter, carbon dioxide is caused to flowthrough the core to gel the sodium silicate. In order that properlyuniform hard cores is made, the carbon dioxide must reach all parts ofthe core and must displace the air in the pores between the sandparticles. In this process it is particularly necessary that the ventsremain open and in an unplugged condition, otherwise the air in someportions of the core is not displaced with the carbon dioxide, and asoft core results.

In another type of cold core-making process, sand and an oil containinga polyalcohol, such as a glycol, is air blown into the mold cavity.Thereafter a diisocyanate, as for example methylene bis (phenyleneisocyanate) or 2,4-toluenediisocyanate is blown through the pores of thecore to set the binder oil into a cross'linked condition. Here again theopenings of the vents must be kept open if soft cores are to be avoided.

Still other cold methods of making cores involving blowing gases throughthe sand and binder have been, and will be developed, and in all ofthese processes it is critical that the passages through the ventsremain open.

The prior art in a few instances has attempted to make a self-cleaningcore vent. The self-cleaning core vents with which I am familiar involveopenings in plates which are appreciably thicker than the particle sizeof the sand that is to be retained. In a few instances, these prior artattempts have utilized yieldable members, but while the members havebeen yieldable, they have been so stiff and heavy that the frequency ofvibration has been too low to be set into vibration by air escapingthrough the vent. What is more, the movement of the thick members hasusually only resulted in the repositioning of the sand particles tofurther embed them between the side edges of the relatively movingparts. In the Dudzinski U.S. Pat. No. 2,482,330 for example, each coilof the spring has limited movement relative to the adjacent coil becauseof the substantial nature of the structure, and relative movement ofthese coils merely allows the sand to be repositioned and in someinstances only further embedded between the deep side edges of each ofthe adjacent coils. Furthermore, the long length of spring that isprovided has a natural frequency that can never be in tune with thenatural pulses which are created by the passage of air through the vent.

In prior art U.S. Pat. No. 3,214,803, air passages through the vent areprovided between a disk and the sidewalls of the vent. Downward movementof the disk is prevented by engagement of ears or projections on the lidwith the sidewalls. Vibration, therefore, is prevented or at the bestgreatly restrained.

An object of the present invention is the provision of a new andimproved self-cleaning vent wherein the air passages through the venthave a depth no greater than the particle size of the sand that is to beretained.

Another object of the invention is the provision of a new and improvedvent of the above described type wherein the air passages are providedbetween fingers cantilevered in openings through a plate structure.

A further object of the invention is the provision of a new and improvedvent of the above described type wherein the side walls of the fingersand the slot in which they are positioned diverge from each other in thedirection of air flow.

A still further object of the invention is the provision of a new andimproved vent wherein the fingers are made of a bimetallic materialwhich is flexed upon a change in temperature.

A still further object of the invention is the provision of a new andimproved method of making a core vent and the like in which the fingersare made integrally with the material in which the openings are formedby etching an irregularly shaped opening through the metal surroundingthe fingers.

Further objects and advantages of the invention will become apparent tothose skilled in the art to which the invention relates form thefollowing description of several preferred embodiments described withreference to the accompanying drawing forming a part of thisspecification.

SUMMARY OF THE INVENTION The gas passages through the vents of thepresent invention are formed by elongated openings through sheetmaterial with at least one side edge of the elongated opening beingdefined by a flexible finger. The elongated opening has a width lessthan the particle size of the material to be retained, and the sheetpreferably has a thickness that is approximately equal to or less thanthe particle size of the material to be retained. The fingers arecantilevered in a flexible manner to permit relative movement withrespect to the opposite sidewall of the passageway through the sheet,and the cantilevered support is preferably provided at one end of thefingers. The fingers preferably act like a reed and are vibrated by thepassage of air through the passageways bordered by the fingers. In someinstances the sidewalls of the passageways including the side edges ofthe fingers diverge toward the downstream end of the air passages, andin some instances the fingers are made of a bimetallic material so thatchanges in temperature will provide relative movement between thefingers and the sidewalls of the openings to free the particles whichmay become lodged between the side walls of the passageways.

The fingers are preferably an integral part of the sheet and are formedby an opening or slit which zigzags back and forth to form fingersalternate ones of which project in opposite directions. The vents arepreferably made by acid etching one or more zigzag openings through athin metal plate. The etching may be accomplished from both sides of theplate, but is preferably accomplished fon'n one side only, to providethe above referred to tapered opening.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic sectional viewthrough an assembled core box and depicts the process of blowing cores;

FIG. 2 is a plan view of a vent plate embodying the present invention;

FIG. 3 is a plan view of another embodiment of vent plate;

FIG. 4 is a sectional view taken approximately on the line 4-4 of FIG.2;

FIG. 5 is a schematic sectional view showing the acidetching processwhich is used to produce the vents of the present invention.

FIG. 6 is a fragmentary view of another embodiment;

FIG. 7 is a plan view on another embodiment of vent;

FIG. 8 is a sectional view taken approximately on the line 8-8 of FIG.7; and

FIG. 9 is a plan view similar to FIG. 7 but showing another embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the principal uses ofthe vents of the present invention will be the venting of air blown coremolds and the like as depicted in FIG. 1 of the drawing. In the processof air-blowing cores, a mixture of sand and binder I0 is blown from apressure reservoir 12 through an orifice 14 in a blow plate 16 into thecavity 18 of a core mold 20. The air that is displaced form the cavity18 by the sand and binder exits through the self-cleaning vents 22 ofthe present invention. The vents 22 are positioned in openings 24 whichcommunicate the cavity 18 to the atmosphere. The vents 22 are usuallypositioned to vent the portions of the cavity 18 which are the last tobe filled by the sand and binder blown into the cavity, to prevent airfrom being trapped in the cavity and the cavity, therefore, not beingcompletely filled with sand and binder. If the cavity is not completelyfilled, soft spots" in the cores are produced, and cores having softspots" cannot be used in the metalcasting operation. During the finalstages of compaction of sand and binder into the cavity 18, the sand andbinder is compacted against the surface of the vents 22. The vents 22 ofthe present invention have a smooth end surface and do not leave animprint in the finished core.

One embodiment of the present invention is shown in FIGS. 2 and 4 of thedrawing. The vent 22 generally comprises a tubular body portion 26having a shoulder 28 formed in its upper end by means of an internalcounterbore 30. A thin sheet or reed plate 32 is positioned againstshoulder 28 and the thin sidewall section 36 opposite the counterbore 30is rolled over into a stepped portion 34 of the reed plate 32, so thatthe top edge 38 of the rolled over portion is flush with the outersurface of the reed plate 32. The tubular body portion 26 is retained inits opening 24 by a slight interference therewith.

The fluid flow passage of the vent 22 shown in FIG. 2 is made by one ormore zigzag openings 40 two shown in the drawing through the thin diskor reed plate 32. The zigzag openings 40 have a width which is less thanthe particle size of the sand to be retained by the vent. Each zigzagopening 40 has generally parallel portions 42 which separate side edgesof fingers 44, and connecting generally right angle portions 46 at thefree ends of the fingers 44. The opposite end of the fingers 44 isunsevered from the main portion of the reed plate 32 and provides acantilevered support for the fingers 44. In the embodiment shown in FIG.2, one zigzag opening 40 starts adjacent one side of the reed plate andzigzags back and forth between a median strip 48, which extends acrossthe major diameter of the plate 32, and a circumferential strip 50. Theopenings 40 may be opposite hand to each other, but in the embodimentshown in FIG. 2 have their generally right angle portions 46 staggeredso that opposite fingers face generally in the same direction. Thisarrangement causes a finger on one side the median strip 48 to be freeof the median strip while the fingers on the opposite side of the medianis supported by the median strip 48. This arrangement produces atwisting action in the median strip 48 opposite the free end of theopposed finger which is helpful in some instances in providing anadditional freeing action for particles which become lodged adjacent themedian strip 48. The preferred form of reed plate 32 will have athickness that does not appreciably exceed the thickness of the particlesize of solids to be retained by the vent. In the embodiment shown inFIG. 2, the vent has a diameter of one half inch and the reed plate hasa thickness of 0.015 inch. The opening has a width that is 0.015 inchand the sand which is to be retained by the vent has an average particlesize of 0.020 inch. This vent has adequate strength to withstand blowingpressures up to approximately 500 pounds per square inch.

The embodiment shown in FIG. 3 is generally similar to that shown inFIGS. 2 and 4, but dilfers principally therefrom in the configuration ofthe openings 40 that are provided. Those portions of the embodimentshown in FIG. 3 which correspond to portions shown in FIGS. 2 and 4 aredesignated by a like reference numeral characterized further in that asuffix a" is affixed thereto. In the embodiment shown in FIG. 3, thezigzag openings 40 extend radially to cover generally pieshaped sectionsthat are separated by radially extending median strips 52. ,Theembodiment shown in FIG. 3 has six openings 40 which are separated bysix radial median strips 52 which join at the center. The median strips52 in effect fonnthree diametrically extending reinforcing members, andthe vents so formed withstand pressures up to approximately 750 poundsper square inch.

The vents of the present invention are preferably made by theacid-etching process depicted in FIG. 5. The reed plate 32 can be madeof any suitable metal, and because stainless steel is strong andresistant to corrosion, it is a preferred material. A stainless sheet ofa desired thickness is coated with a photographic resist" material 54. Aphotographic negative is laid over the surface of this material, and alight is passed through the light-transmitting portions of the negativeto strike the photographic resist material. The photographic negativehas light-transmitting portions corresponding with the openings 40, andthe light struck portions of the resist" layer 54.

In the embodiment shown in FIG. 5, the metal is 0.015-inch thick, andthe openings 56 in the resist layer 54 are approximately 0.008 inches.In the embodiment shown in FIG. 6,

openings 56 are positioned on both sides of the plate 32 opposite eachother, and the acid-etching processing is performed form both sides ofthe plate. In the embodiment shown in FIG. 5, however, the openings 56are provided in only the bottom layer of the resist material 54 and theacid etching proceeds from the bottom only. Using this technique andstock 0.015-inch thick, the openings 40 are 0.0l6-inch wide adjacent theholes 56 and are 0.0l2-inch wide at the opposite side of the plate. Theplates etched form the bottom side only are installed in the vents withthe widest portion of the openings 40 facing inwardly of the vent, andwith the narrow portions of the openings 40 facing outwardly where theyare engaged by the sand particles to be retained. In the resist layers54 are positioned directly opposite each other and the shoulder 34 isformed by removing a circumferential strip 58 of the resist material 54around the plate 32 on its top surface only. A proper groove istherefore provided for receiving the turned over edge 38 as shown inFIG. 4.

Plates having openings of various widths can be made using the samephotographic plate by varying the duration of the acid etching.Similarly, vents of various strengths can be made using the samephotographic plate by varying the thickness of the plate that is etched.

A preferred embodiment is produced by using a strip material for thereed plate 32 which is a laminated or bimetallic material whose bottomlayer has a coefficient of expansion which is greater than that of itstop layer. Preferably the two layers of the bimetallic sheet materialare stainless steels of different composition arranged so that thebottom layer has the greatest coefficient of expansion. These materialscan be etched satisfactorily and will provide fingers which flexupwardly against the flow of sand and air when the reed plate 32 isheated.

In the preferred method of use of the vents of the present invention,the bimetallic embodiments are positioned as above described and areheated to around 200 F. temperature prior to the time that the moldcavity 18 is filled with the sand. The lengths of the fingers are suchthat they will be deflected upwardly form the upper surface of the plate32 by approximately 0.002 inch at a temperature of approximately 200 F.In the embodiment shown in FIG. 2, 90 p.s.i. air pressure on the fingersdeflects the fingers downwardly by approximately the same amount, sothat they are substantially parallel with the top surface of the plate32 when the core material is compacted thereagainst at the elevatedtemperature. The cold sand and resin which engages the vent reduces thetemperature of the vent to approximately 200 F. The vent is then heatedto a temperature of between 400600 F. to cure the binder. When thefinished core is removed form the mold 20, the fingers flex outwardlyapproximately 0.005 inch and thereafter the temperature of the ventagain decreases to approximately 200 F. This flexing of the fingersdislodges any sand that has been embedded in the upper end of theopenings 40. It will be seen that the embodiment shown in FIG. 2 hasfingers with free ends adjacent supported sections of the plate so thatmaximum relative movement is provided in these areas. It will also beseen in FIGS. 2 and 3 that the fingers are arranged adjacent to eachother so that a free end on one finger is always adjacent thecantilevered end of an adjacent finger. This provides maximum relativemovement therebetween for dislodging sand particles.

A further advantage of the invention is had by the reed effect which isproduced when high-pressure air is blown through the passages 40. Thelengths of the fingers are such as to have sufficient flexibility tovibrate when air or other gas escapes through the opening 40. The reedeffect causes what would be small static deflections to build up intolarge oscillations which remove sand particles from the openings.

Still other designs of vent plates can be made having fingers of evengreater flexibility. The embodiments shown in H68. 7 and 8 is generallysimilar to that shown in FIGS. 2 and 4, but differs principallytherefrom in that there is no median strip, and that the fingers runacross the width of the disk, so that they are approximately twice aslong as those shown in FIGS. 2 and 4. Those portions of the embodimentshown in FIGS. 7 and 8 which are similar to corresponding portions ofthe embodiment in FIGS. 2 and 4 are designated by the same referencenumeral characterized further in that a suffix b" is affixed thereto.

in the embodiment shown in FIGS. 7 and 8 the peripheral strip 50b isnarrower than in the embodiment shown in FIGS. 2 and 4, so that theouter edges of the openings 40b are positioned over the sidewalls of thetubular body portion 26b. The tubular portion 26b is provided with ashoulder or abutment 60 on its inside walls beneath the disk 32b. Theshoulder 60 projects radially inwardly by a distance greater than thewidth of the openings 40bto provide an abutment on which the fingers 44bmay hear. The shoulder 60 is positioned beneath the disc 32b by adistance which permits normal vibration of the fingers Mbbut whichprevents their being deflected by a distance which will producepermanent defonnation or damage to the fingers. The fingers 44b arecantilevered form the peripheral strip 50b and extend across the disk,then arcuately around the disk with their outer edges positioned overthe top of the shoulder 60, and then back across the disk. A secondfinger starts at a position on the opposite side of the disk andproceeds similarly, with its back-tumed portion being positioned withinthe U of the other finger 44b. The fingers 4412 have a period ofvibration that is approximately in tune with the frequency of thevibrations of air vented through the openings 40b. The configurationshown in FIG. 7 is preferably used in small size vents, as for examplethose having an outside diameter of one-quarter inch.

The embodiment shown in FIG. 9 is similar to the embodiment shown inFIGS. 7 and 8 in that it is provided with a shoulder 60c for limitingdeflection of the fingers 44c. The embodiment shown in FIG. 9 differsfrom the embodiment shown in FIG. 7 principally in that the fingers arecantilevered from a median strip 480. Those portions of the embodimentshown in FIG. *9 which are similar to portions of the embodimentspreviously described are designated by a like reference numeral.characterized further in that a sufiix 0" is affixed thereto. Theconfiguration shown in FIG. 9 is likewise preferably used for smallersize vents, as for example those having a diameter of approximatelyone-quarter inch.

The construction can also be thought of as comprising fin gerspositioned in slots, or opening portions through a sheet structure, aswould occur where the fingers are not made integral with the sheetstructure containing the slots or opening portions.

While the invention has been described in considerable detail, I do notwish to be limited to the particular embodiments shown and described,and it is my intention to cover hereby all novel adaptations,modifications, and arrangements thereof which come within the practiceof those skilled in the art to which the invention relates, includingthe use of the vents in the forming and or molding of plastic foams,beads etc.

I claim:

1. A vent and the like for confining particulate material of generallypredetennined size, comprising: a support member, a thin sheet offlexible material secured to said support member, a plurality ofgenerally parallel opening portions through said sheet, and a pluralityof generally parallel fingers positioned in said opening portions toprovide flow passages through said sheet which are bordered by saidfingers and which flow passages have a width that is less than thepredetermined size, and whereby flexure provides relative motion betweenthe fingers and the sidewalls of said opening portions.

2. The vent of claim 1 wherein said flexure is provided by airflowthrough said flow passages.

3. The vent of claim 1 wherein said flexure is provided by thermalexpansion.

4. The vent of claim 1 wherein said sheet is less than approximately0.020-inch thick and said flow passage is wider ad jacent one side ofsaid sheet than it is adjacent the other side of said sheet.

5. A vent and the like for confining particulate material of generallypredetermined size, comprising: a support member, a thin sheet offlexible material secured to said support member, said sheet having atleast one long narrow opening therethrough which repeatedly reversesdirection to form a plurality of generally parallel spaced apartoppositely extending side by side fingers, and said opening having awidth that is less than the predetermined size.

6. The vent of claim wherein adjacent ones of said fingers arecantilevered form opposite ends from each other.

7. The vent of claim 5 wherein said support has a shoulder positionedbeneath at least one of said fingers, said shoulder having clearancewith said finger in the undeflected condition of the finger and beingadapted to limit deflection of said fingets.

8. The vent of claim 5 wherein said sheet has an integral portionextending across said support member, with integral fingers projectinggenerally perpendicularly form opposite sides of said integral portion.

9. The vent of claim 8 in which said integral portion is unsupportedexcept adjacent opposite sides of said support so that said integralportion acts as torsion member.

10. The vent of claim 9 wherein the fingers on opposite sides of saidintegral portion are alternately spaced.

1]. The vent of claim 6 wherein said sheet is circular, said sheethaving at least two radial integral portions intersecting at the centerof the circular sheet, each integral portion having integral fingersprojecting towards the other integral portion with the fingers on oneintegral portion being positioned between the fingers of the otherintegral portion.

12. The vent of claim 11 having three evenly spaced integral portionseach having oppositely projecting fingers positioned between fingers ofthe adjacent integral portions.

13. The vent of claim 12 wherein the fingers are arcuately shaped andare parallel to the periphery of said circular sheet.

14. The vent of claim 1 having upstream and downstream faces and whereinsaid sheet is a bimetallic laminate.

15. The vent of claim 14 wherein said opening is wider at the downstreamface than at the upstream face.

16. The vent of claim 15 wherein the layer forming the downstream facehas the greatest coefficient of expansion.

17. The vent of claim 16 wherein said sheet has an integral portionextending across said support member, with integral fingers projectinggenerally perpendicularly from opposite sides of said integral portion.

18. The vent of claim 17 wherein said sheet is circular and has at leasttwo radial integral portions intersecting at the center of the circularsheet, each integral portion having integral fingers of one integralportion being positioned between the fingers of the other integralportion.

19. A vent and the like for confining particulate material of generallypredetermined size, comprising: sheet material having upstream anddownstream sides and spaced-apart elongated slots therethroughcommunicating said sides, and a plurality of cantilevered fingersrespective ones of which are positioned in respective ones of said slotswith their upstream surface generally parallel with the upstream surfaceof said sheet material around said slots and with the clearance betweensaid fingers and sides of said slots being less than said predeterminedsize, said fingers being cantilevered in flexible fashion to providerelative movement with the side surfaces of said slots.

20. The vent of claim 19 wherein said fingers and sheet material areintegrally connected.

21. The vent of claim 19 wherein said fingers are supported incantilever fashion adjacent end portions of said slots.

22. The vent of claim 21 wherein said fingers have a thicknesssubstantially no greater than said predetermined thickness.

1. A vent and the like for confining particulate material of generallypredetermined size, comprising: a support member, a thin sheet offlexible material secured to said support member, a plurality ofgenerally parallel opening portions through said sheet, and a pluralityof generally parallel fingers positioned in said opening portions toprovide flow passages through said sheet which are bordered by saidfingers and which flow passages have a width that is less than thepredetermined size, and whereby flexure provides relative motion betweenthe fingers and the sidewalls of said opening portions.
 2. The vent ofclaim 1 wherein said flexure is provided by airflow through said flowpassages.
 3. The vent of claim 1 wherein said flexure is provided bythermal expansion.
 4. The vent of claim 1 wherein said sheet is lessthan approximately 0.020-inch thick and said flow passage is wideradjacent one side of said sheet than it is adjacent the other side ofsaid sheet.
 5. A vent and the like for confining particulate material ofgenerally predetermined size, comprising: a support member, a thin sheetof flexible material secured to said support member, said sheet havingat least one long narrow opening therethrough which repeatedly reversesdirection to form a plurality of generally parallel spaced apartoppositely extending side by side fingers, and said opening having awidth that is less than the predetermined size.
 6. The vent of claim 5wherein adjacent ones of said fingers are cantilevered from oppositeends from each other.
 7. The vent of claim 5 wherein said support has ashoulder positioned beneath at least one of said fingers, said shoulderhaving clearance with said finger in the undeflected condition of thefinger and being adapted to limit deflection of said fingers.
 8. Thevent of claim 5 wherein said sheet has an integral portion extendingacross said support member, with integral fingers projecting generallyperpendicularly from opposite sides of said integral portion.
 9. Thevent of claim 8 in which said integral portion is unsupported exceptadjacent opposite sides of said support so that said integral portionacts as a torsion member.
 10. The vent of claim 9 wherein the fingers onopposite sides of said integral portion are alternately spaced.
 11. Thevent of claim 6 wherein said sheet is circular, said sheet having atleast two radial integral portions intersecting at the center of thecircular sheet, each integral portion having integral fingers projectingtowards the other integral portion with the fingers on one integralportion being positioned between the fingers of the other integralportion.
 12. The vent of claim 11 having three evenly spaced integralportions each having oppositely projecting fingers positioned betweenfingers of the adjacent integral portions.
 13. The vent of claim 12wherein the fingers are arcuately shaped and are parallel to theperiphery of said circular sheet.
 14. The vent of claim 1 havingupstream and downstream faces and wherein said sheet is a bimetalliclaminate.
 15. The vent of claim 14 wherein said opening is wider at thedownstream face than at the upstream face.
 16. The vent of claim 15wherein the layer forming the downstream face has the greatestcoefficient of expansion.
 17. The vent of claim 16 wherein said sheethas an integral portion extending across said support member, withintegral fingers projecting generally perpendicularly from oppositesides of said integral portion.
 18. The vent of claim 17 wherein saidsheet is circular and has at least two radial integral portionsintersecting at the center of the circular sheet, each integral portionhaving integral figers projecting towards the other integral portionwith the finger of one integral portion being positioned between thefingers of the other integral portion.
 19. A vent and the like forconfining particulate material of generally predetermined size,comprising: sheet material having upstream and downstream sides andspaced-apart elongated slots therethrough communicating said sides, anda plurality of cantilevered fingers respective ones of which arepositioned in respective ones of said slots with their upstream surfacegenerally parallel with the upstream surface of said sheet materialaround said slots and with the clearance between said fingers and sidesof said slots being less than said predetermined size, said fingersbeing cantilevered in flexible fashion to provide relative movement withthe side surfaces of said slots.
 20. The vent of claim 19 wherein saidfingers and sheet material are integrally connected.
 21. The vent ofclaim 19 wherein said fingers are supported in cantilever fashionadjacent end portions of said slots.
 22. The vent of claim 21 whereinsaid fingers have a thickness substantially no greater than saidpredetermined thickness.